diff --git a/all-is-cubes/src/lib.rs b/all-is-cubes/src/lib.rs
index 15f04e7db..c56075a50 100644
--- a/all-is-cubes/src/lib.rs
+++ b/all-is-cubes/src/lib.rs
@@ -3,6 +3,7 @@
 #![feature(large_assignments)]
 #![move_size_limit = "2000"]
 #![feature(let_chains)]
+#![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(trait_upcasting)]
 #![feature(try_blocks)]
diff --git a/all-is-cubes/src/space/space_txn.rs b/all-is-cubes/src/space/space_txn.rs
index 6c8b9f0ea..5c2f991ed 100644
--- a/all-is-cubes/src/space/space_txn.rs
+++ b/all-is-cubes/src/space/space_txn.rs
@@ -477,6 +477,8 @@ pub struct CubeTransaction {
     fluff: Vec<Fluff>,
 }
 
+impl !Transaction for CubeTransaction {}
+
 impl fmt::Debug for CubeTransaction {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let Self {
diff --git a/all-is-cubes/src/transaction/generic.rs b/all-is-cubes/src/transaction/generic.rs
index 64f8ba872..7c1304328 100644
--- a/all-is-cubes/src/transaction/generic.rs
+++ b/all-is-cubes/src/transaction/generic.rs
@@ -50,6 +50,8 @@ impl<K: fmt::Debug, C> fmt::Display for MapConflict<K, C> {
     }
 }
 
+impl<K, V> !Transaction for BTreeMap<K, V> {}
+
 impl<K, V> Merge for BTreeMap<K, V>
 where
     K: Clone + Ord + fmt::Debug + 'static,
@@ -105,6 +107,8 @@ where
 
 macro_rules! hashmap_merge {
     ($module:ident) => {
+        impl<K, V, S> !Transaction for $module::HashMap<K, V, S> {}
+
         impl<K, V, S> Merge for $module::HashMap<K, V, S>
         where
             K: Clone + Eq + Hash + fmt::Debug + 'static,